Among numerous other uses, high energy density batteries find various applications in back-up power systems, electric and hybrid vehicles, and consumer electronics. Exemplary applications include data loggers that make measurements in difficult environments (e.g., ocean floor or high altitudes) and larger stand-alone instrumentation (e.g., backup power sources for telephone lines).
Batteries typically comprise two major components, electrodes (an anode and a cathode), and an electrolyte. The electrodes can be viewed as the phase through which charge is carried by electronic movement, and typical electrodes include metals or semiconductors, but may also be solid or liquid. The electrolyte can be viewed as the phase through which charge is carried by the movement of ions. Electrolytes may be any phase on the continuum of liquid to solid, including gels, pastes, fused salts, or ionically conducting solids, such as sodium beta-alumina, which has mobile sodium ions (Bard, Allen J. and Larry R. Faulkner, Electrochemical Methods: Fundamentals and Applications, John Wiley & Sons (New York), 1980).
The individual components of batteries are constantly being investigated for materials and methods that will improve the energy density of the battery, increase the efficiency of the battery, and improve the safety aspects of the use and storage of the battery and its components. Table 1 shows the specific energy densities of exemplary known battery systems.
TABLE 1SPECIFIC ENERGY DENSITY OF MAJOR BATTERY SYSTEMS(1)SPECIFIC ENERGY (WH/KG)PRIMARY BATTERYZn/air370Li/SOCl2590Li/SO2260Li/MnO2230Li/FeS2260Li/(CFx)n250Li/I2245SECONPARY BATTERYLithium-ion150Lithium/iron disulfide2180Sodium/sulfur21701D. Linden and T. B. Reddy, “Handbook of Batteries”, 3rd edition (2001)2High temperature batteries.
In addition to these major battery systems, other experimental high energy density batteries are being developed. An example is the lithium/water battery. Prototype lithium/water batteries using a 30-cm diameter, 30-cm thick solid cylindrical lithium anode with a weight of 11.5 Kg have been designed to deliver 2 W at 1.4V for about one year with a specific energy of 1800 to 2400 Wh/Kg, based on lithium only since the water is continuously pumped to the anode. Various patents have disclosed the use and modification of lithium-water batteries (see e.g., U.S. Pat. No. 5,376,475 issued to Ovshinsky et al.; U.S. Pat. No. 5,427,873 issued to Shuster; U.S. Pat. No. 4,001,043 issued to Momyer; U.S. Pat. No. 4,709,882 issued to Galbraith). Generally, lithium has been the anode material of choice for these batteries because of its high voltage, reactivity, high capacity and low equivalent weight. However, the addition of water to lithium batteries has proven to lower the specific energy and efficiency of the battery relative to other similar batteries.
Lithium/water batteries also produce hydrogen gas as a product of the electrochemical reaction in the cells. The production of hydrogen gas creates an explosion hazard and is, therefore, considered highly unsafe. The lithium/air and aluminum/air batteries have the highest theoretical specific energy and good efficiency, but air needs to be fed to the cathode in order for the battery to operate. There are other combinations of materials that are used in a “sealed” battery—such that air cannot reach or “be fed” to the cathode. Lithium/hydrogen peroxide batteries generally employ the following electrochemical cell reaction:2Li+H2O+H2O2 2LiOH*H2O.
Although the lithium/hydrogen peroxide battery does not electrochemically produce any hydrogen gas in significant quantities, it nevertheless includes hydrogen peroxide, which is inherently unstable and is known to decompose with the release of oxygen even at room temperature. On the other hand, lithium may chemically react with water in a parasitic corrosion reaction that produces no electricity but produces hydrogen. This release of oxygen and hydrogen makes the lithium hydrogen peroxide battery intrinsically unstable. Therefore, there is still a need to develop batteries that have a relatively high specific energy density, have high efficiencies, can be sealed, are intrinsically more stable, and are relatively safe to store and operate.